What is Plano-convex ingot?

Plano-convex ingots are lumps of metal with a flat or slightly concave top and a convex base. They are sometimes, misleadingly, referred to as bun ingots which imply the opposite concavity. They are most often made of copper, although other materials such as copper alloy, lead and tin are used. The first examples known were from the Near East during the 3rd and 2nd Millennia BC. By the end of the Bronze Age they were found throughout Europe and in Western and South Asia. Similar ingot forms continued in use during later Roman and Medieval periods.